Device for intermittent gas-lift exploitation of oil wells

ABSTRACT

A device for the intermittent exploitation of gas-lift oil wells lines with a casing seals the lower portion of the casing from the upper portion except through a valved passageway. The valve is a flexible diaphragm communicating with an oleo-pneumatic chamber through capillary orifices so that when gas under pressure is supplied from the surface, the flow of liquid through the capillary orifices delays the opening of the valve.

llnitefl States Patent 1 Szilas et al.

DEVICE FOR INTERMITTENT GAS- LIFT EXPLOITATION OF OIL WELLS Inventors: A. Pal Szilas; Janos Bognar; Bela Mating; Laszlo Bajoczlry, all of Miskolc, Hungary Assignee: Nagyalfoldi Koolaj-es lFoldgaztermelo Vallalat, Szolnok, Hungary Filed: Apr. 29, 1971 Appl. No.: 138,543

417/112 lnt. Cl. ..F04f 1/06, F041" 3/00, Fl6k 15/00 Field of Search ..417/118, 143, 112,

11] amas 1 May 8, 1973 [56] References Cited UNITED STATES PATENTS 3,213,806 10/1965 Walton ..417/112 Primary Examiner-Carlton R. Croyle Assistant Examiner-Richard E. Gluck Attorney-Young & Thompson A device for the intermittent exploitation of gas-lift oil wells lines with a casing seals the lower portion of the casing from the upper portionexcept through a valved passageway. The valve is a flexible diaphragm communicating with an o1eo-pneumatic chamber through capillary orifices so that when gas under pressure is supplied from the surface, the flow of liquid through the capillary orifices delays the opening of the valve.

ABSTRACT 4 Claims, 1 Drawing Figure DEVICE FOR INTERMITTENT GAS-LIFT EXPLOITATION OF OIL WELLS lntermittent exploitation of gas-lift oil wells is made use of, as a rule, with wells of low productivity and low formation pressure. The essence of the process is that liquid collected in the well from the formation is elevated to the surface more or less in the shape of a plug by means of gas forced into the well, which serves as a gas-lift. The simplest known device for this purpose is a tubing incorporated in the well without any apparatus and reaching as deep as the well bottom. Gas is forced from the surface into the annulus so that it can lift the oil through the tubing. With this simple variant of well construction specific gas consumption is rather high as, after the lifting of the liquid plug to the surface, a relatively large quantity of input gas left in the well escapes to the surface.

With modern intermittent gas-lift oil wells the annulus is closed above the well bottom with a packer, the gas being forced into the tubing through orifices above the packer and equipped with gas-lift valves. When the gas has lifted the liquid plug to the surface, the valve stops the further supply of gas. Thus, when the oil plug has been lifted to the surface, only the input gas filling the tubing of relatively small volume will escape to the surface. For this reason, specific gas consumption of such devices is low.

Quite a few new gas-lift valves called pressure-controlled valves have been developed lately. Such valves are opened and closed by slight variations of inputgas pressure on the surface. The shape of the majority of the devices that of a tube of small diameter operated by a metal bellows and mounted on the outer pipe wall; i.e., of a size that can be accommodated in the cross section of the annulus. Their drawback is that, for reasons of well completion, they are of small diameter, owing to which their gas throughput is low and the lifting of the plug to the surface is slow; a considerable part of the liquid trickles back into the well and, consequently, lifting efficiency is poor. Gas feeding cross section is greater with the known rubber diaphragm valves. They are ring-shaped, surrounding the tubing. A disadvantage of this system consists in that it opens at the same pressure at which it closes. Therefore, when gas is injected into the system at a pressure slightly higher than operation-pressure, the valve opens and lets gas stream into the tubing. If, on the other hand, input gas flows from the surface at a slower rate, a greater amount of gas will enter the tubing per unit time than the quantity of gas streaming into the annulus from above. Pressure in the annulus drops and causes the gas-lift valve to close. Oil already lifted falls down again and the efficiency of lifting becomes very poor, and production may completely cease.

An object of the present invention is to provide a high throughput gas-lift device, using a valve with resilient diaphragm preferably a rubber one of easy handling, suitable for use also when input gas streams from the surface into the annulus at a relatively slow rate. This supposes the opening pressure of the valve to be superior to the closing pressure.

Thus, the invention is a device for intermittent exploitation of gas-lift wells having a pressure-controlledresilient diaphragm valve with spread and snap action preferably with a rubber diaphragm a resilient packer and an intermediate piece fitted with a differential valve, characterized by the fact that the valve chamber that can be put under pressure behind the diaphragm is divided into two parts by an inner partition. This partition has larger orifices equipped with check valves and smaller, capillary ones, the double space being filled with neutral pressure-transmitting liquid of low vapor pressure. For pressure transmitting purposes silicone oil is preferably used. The valve chamber is put under pressure by means of a gas, e.g. nitrogen gas. According to a preferred form the invention, the gas-lift valve, the resilient packer, which is preferably made of rubber, and the fitting form a single unit, the mounting of which is in the well does not require any special skill.

The device as a single unit can be mounted on the tubing in the known manner. The resilient rubber packer, like other devices of similar function, bears, when closing, against the tubing that reaches as deep as the well bottom, the weight of the tubing above the packer compressing the rubber gaskets and forcing them against the annulus. In case the well bottom is loose, it eventually subsides under the pressure of the tubing with the latter following and causing the packer to open. According to the invention, the fitting has a lock which prevents the packer from opening again, once it has shut, even if the well bottom subsides.

The details of the invention are illustrated by the description of its operation, with reference to the accompanying diagram of one of the preferred embodiments. The accompanying drawing shows the device mounted on the tubing and lowered into the well, in

longitudinal section.

Before mounting in the well, the double space of the device is filled on the surface with about 200 cm of ne utral pressure-transmitting liquid of low vapor pressure, preferably with silicone oil, through filling orifice 2 pt valve chamber 1; then the chamber is filled with nitrogen gas under pressure. Under the effect of the gas pressure in the chamber, rubber diaphragm 4 closes against input gas inlet orifices 3 and 3a and keeps them shut. When assembled, tubing pipe 14 corresponding to the required well chamber length is mounted under the equipment. With the tubing reaching well bottom 12, the weight of the pipe bearing heavily on the device compresses the rubber gaskets 5 of the packer and the gaskets are forced against the casing wall. Thus, under the packer, a chamber 10, closed against communication with the surface, is formed. At the same time as the compression of gaskets 5, sliding claw wedges 7 fasten tubing length 14 to fitting 8 and prevent its being displaced from this relative position. Rubber gaskets 5 keep closing even if well bottom 12 subsides. Now the device is in working condition. When a sufficient amount of time has passed for a quantity of oil to have collected in chamber 10, a surface time cycle controller injects gas into annulus 13. Rubber diaphragm 4 opens when the pressure in annulus 13 has exceeded the pressure in valve chamber 1 by about 30 psi. The building up of an overpressure of 30 psi takes one and a half minute. This takes place by the silicone oil behind the rubber diaphragm oozing into the inner chamber space through capillary orifice 15 of the partition so as to permit the rubber diaphragm to open. Oozing time can be controlled by varying the size of capillary orifices 15. When the valve has opened, input gas streams around the rubber diaphragm through orifices 6 into chamber 10. Input gas forces the oil into the tubing through shoe orifice l1 and lifts it to the surface. As soon as input gas pressure at the bottom of annulus 13 drops below the pressure of valve chamber 1, rubber diaphragm 4 is forced into closing position. Instant-shutoff is obtained through the silicone oil being permitted to flow into the outer chamber space not only through capillaries 15 of small diameter but also through big orifices 16 fitted with check valves. A conventional differential valve 9 in fitting piece 8 has the function to allow formation gas streaming into chamber 10 to pass to the tubing while liquid is collecting. Without this arrangement formation gas would fill a considerable part of the well chamber at the expense of the oil storage volume, and this would impede but would not prevent the accumulation of oil in chamber 10. The arrangement and operation of a conventional differential valve is further described in the Cameo Gas Lift Manual", of Camco, lnc., Houston, Tex., 1962, at pages 7-001 and 7-002.

The main advantage of the invention is that it permits an economical exploitation of wells producing from formations having relatively low bottom-hole pressure along with loosely structured poor quality bottoms, when input gas pressure on the surface is subject to oscillations and the gas stream is relatively poor. Another significant advantage is that the device assembles all structural elements needed for the underground well construction in a single unit, owing to which its mounting is safe, simple and inexpensive. it can be economically used with oil wells of low formation pressure and low output that could not be economically exploited with any other production equipment. As it contains no component liable to failure, its service life is long. This represents a considerable cut in 1118i?- tenance cost against any other known machinery.

What we claim is:

1. A device for intermittent exploitation of gas-lift oil wells lined with a casing, comprising resilient packing means sealing a lower portion of the interior of the easing from an upper portion of the interior of the casing, means defining a passageway past said packing means between said upper and lower portions of the interior of the casing, valve means for selectively opening and closing said passageway, said valve means opening when the pressure in the casing above said packing means is above a predetermined minimum, said valve means comprising a flexible diaphragm, a chamber communicating with said diaphragm through at least one capillary orifice, and a quantity of liquid in said chamber above said at least one capillary orifice, said liquid passing through said capillary orifice and pressing on said diaphragm to close said passageway, whereby an increase in the pressure in the interior of said casing above said predetermined minimum causes said liquid to flow through said at least one capillary orifice into said chamber to permit said diaphragm to deflect to open said passageway, and gas-lift means operable by gas passing through said passageway to raise oil from the well by gas-lift action.

2. A device as claimed in claim 1, said chamber being sealed and having a quantity of gas under pressure at the top thereof.

3. device as claimed in claim 1, including tubing extending centrally of the casing below said packing means, said tubing having orifices adjacent the lower end thereof to receive oil and the gas that lifts said oil with said gas-lift action.

4. A device as claimed in claim 3, and sliding claw wedges by which said tubing is suspended from said device. 

1. A device for intermittent exploitation of gas-lift oil wells lined with a casing, comprising resilient packing means sealing a lower portion of the interior of the casing from an upper portion of the interior of the casing, means defining a passageway past said packing means between said upper and lower portions of the interior of the casing, valve means for selectively opening and closing said passageway, said valve means opening when the pressure in the casing above said packing means is above a predetermined minimum, said valve means comprising a flexible diaphragm, a chamber communicating with said diaphragm through at least one capillary orifice, and a quantity of liquid in said chamber above said at least one capillary orifice, said liquid passing through said capillary orifice and pressing on said diaphragm to close said passageway, whereby an increase in the pressure in the interior of said casing above said predetermined minimum causes said liquid to flow through said at least one capillary orifice into said chamber to permit said diaphragm to deflect to open said passageway, and gas-lift means operable by gas passing through said passageway to raise oil from the well by gas-lift action.
 2. A device as claimed in claim 1, said chamber being sealed and having a quantity of gas under pressure at the top thereof.
 3. A device as claimed in claim 1, including tubing extending centrally of the casing below said packing means, said tubing having orifices adjacent the lower end thereof to receive oil and the gas that lifts said oil with said gas-lift action.
 4. A device as claimed in claim 3, and sliding claw wedges by which said tubing is suspended from said device. 